Underwater diving operations for many purposes can be hampered by the lack of visibility due to the turbidity or depth of water in which the diver finds himself. This is especially true if the diver is attempting to locate submerged objects which are some distance away from his current position and cannot be seen. With zero or near zero visibility, a diver also can become confused and disoriented so that he does not know north, south or other directions.
One striking example of the problems encountered by a diver under such circumstances is when he is attempting to locate and remove various man-made objects or debris from the sea bottom sites of offshore oil or gas drilling or production operations that have been temporarily or permanently discontinued. Such bottom site clearance is mandated by federal regulations after offshore drilling or production activities cease at leased government sites on the outer continental shelf (OCS) of the United States. Local and foreign governments also quite often require bottom site clearance in connection with offshore drilling or other underwater activities.
The federal OCS site clearance requirement involves the removal of well heads, drilling rigs and production platforms which are no longer in service, along with other man-made objects including submerged debris on the ocean floor. A major reason for this removal is so that these objects will not conflict or interfere with other uses of the OCS such as shrimp fishing, where boats trawl for fish with nets that can become entangled with man made underwater obstructions. For example, objects or debris that may be found on sea bottom sites where oil or gas activities have been conducted include pipes, tires, batteries, wire rope, hoses, tools, gratings, plates and other structural shapes that have fallen off or have been thrown from platforms or from boats that transport equipment and personnel to and from such platforms. In addition, the stubs of severed platform legs may still project upward from the sea bottom even though such legs are required to be cut off below the mud-line when abandoned platforms are removed from the offshore sites.
When underwater visibility is zero or nearly so to a diver, one widely used search technique for locating and removing such objects from the sea bed has been to provide the diver with a search line of predetermined length, e.g., thirty feet, that is connected to a weight or other structure at a particular sea bed location within the site area to be cleared. The diver, who is usually weighted down, then walks in a circle while holding the line taut, after which another section of line may be added and a circle walked in the opposite direction. Objects that are discovered by visual sighting or by snagging the taut line can then be lifted aboard a surface vessel for eventual disposal on land. This circular procedure is repeated at other sea bed locations until the entire bottom site area has been covered. However, since a bottom site area to be cleared can encompass the area of a circle over 1300 feet in radius from the center of a drilling or production platform, it is apparent that a diver must expend a great deal of time and energy in walking many overlapping small circles while holding a taut line in order to completely traverse such a large site area. This is especially critical when a diver is working at 300 feet where the bottom time is limited to 30 minutes. The majority of oil or gas drilling and production activities are now conducted in this water depth in the Gulf of Mexico off the Texas/Louisiana coastline. The diver then must be brought to the surface in a controlled manner to avoid getting decompression sickness before diving again at some later time. Such interruptions substantially increase the duration of a site clearance operation.
Moreover, if the sea bottom is relatively soft or is overlaid by layers of silt, a diver often finds himself knee-deep in sand or mud while walking which can be physically exhausting. Bottom holes, depressions or other geographical features which cannot be seen also pose some danger to a diver if he unexpectedly encounters them.
Another current search technique is to place a sonar transmitter/receiver transducer on the sea bottom so that sonic waves reflected from the diver and other underwater objects are shown as echo images on a shipboard or other remote station monitor. Based on the location of these monitored images which represent the diver and objects to be recovered, a remote station operator then gives audio commands to the underwater diver via a telephone cable in an effort to guide or direct his movements to these objects. However, such remote audio guidance also has not proven to be particularly efficient either in diver time or effort because of the directional disorientation he experiences due to a lack of visibility.
A U.S. Pat. No. 3,045,206 (Ahrens et al) also shows the use of a self-contained sonic transducer/CRT device which is carried by a diver to help him locate underwater objects whose sonar images he views on the CRT screen that may be either outside or inside his helmet. However, the Ahrens device does not also permit the diver to view a sonar image of himself in relation to other object images, and it has other disadvantages in comparison with the subject invention, including an apparent need for the Ahrens diver also to consult a compass and level that he additionally carries. In U.S. Pat. No. 4,102,203 (Sylvester et al), the signals from an underwater ultrasonic testing transducer operated by a diver are transmitted to a remote station for analysis and visual display, from whence visual image test result signals are sent back to the diver for display on his own monitor; however, the Sylvester system is not designed for or capable of locating the position of underwater objects and directing the diver thereto
Therefore, bottom site clearance in offshore oil and gas fields, as well as many other underwater tasks, have been very exhausting, time consuming and expensive operations when low or zero visibility prevents a diver from seeing and going directly to an underwater object. Until development of the subject invention, however, it has not been possible to give a diver any significant directional help in finding his way to underwater objects under such conditions.